enhancements: app icon and configuration of the period of interest

[RJVB]

Please find attached 2 patches:

- patch-qarte3-app-icon.diff sets the application and window icons at runtime, allowing the application to show up with its own icon instead of the generic Python icon

- patch-qarte3-scan-period.diff adds a configuration option allowing to specify the period of interest (in days) over which Qarte should look for available videos. This provides an answer to my question (https://answers.launchpad.net/qarte/+question/473994).
I've tested a period of 62 days and been able to download over the full period.

[VinsS (vincent-vandevyvre)]

App icon added in revision 177. Thanks.

For the number of pages parsed by Qarte I've fixed the maximum at 14 pages.
This is a good compromise between the video's choice and the time necessary to parse the pages and download all the thumbnails.

Qarte keep in cache the video's data, so this morning I've in Qarte a choice of 344 videos and the oldest are dated the Dec. 09 2016 (76 days!).

[RJVB (rjvbertin)]

Yeah, I understood you fixed the maximum, and why, so I preserved your default. The cache mechanism still works, so even with my tweak you only have to wait a bit longer (or less long if you shorten the period!) the 1st time the new search is executed. Afterwards startup is just as fast as with the default 14 days setting.

Keeping video references in cache over time is nice, but of little value to people who just start using the application (ever, or on a new machine/account), or who use it only sporadically (or who lost the cache for whatever reason).

It was easy enough to implement the configurable scanning period so if this were my code I would never consider imposing my own ideal compromise over the users' better knowledge of their own needs. Of course, if you know the upper limit in days above which Qarte no longer provides any videos that's something that can easily be imposed by setting the spinbox maximum.

[RJVB (rjvbertin)]

Re: the app icon: icons are expected to be rectangular. I didn't realise this myself, but you may find that the icon renders better in all situations if you create a rectangular version and use that. I've attached an example, made by adding margins (1 pixel to the left, 34 top and bottom).